Section 8: Columns for Single Column Bents or Piers
Materials
Use concrete with a minimum
3.6 ksi and Grade 60 reinforcing steel. Higher concrete strengths may be used if needed in special cases.
3.6 ksi and Grade 60 reinforcing steel. Higher concrete strengths may be used if needed in special cases.
Mass concrete may be needed depending on the size of the column.
Higher reinforcing steel grades may be used provided their use satisfies requirements in AASHTO.
Geometric Constraints
Consider using hollow pier sections where appropriate. Hollow piers subject to the vehicular collision load must be protected from the collision consistent with the protection requirements elsewhere in this manual.
Structural Analysis
Account for second-order effects, with the structural model accounting for reduced stiffness from a cracked section.
Deflections from an analysis need to be consistent with boundary conditions of the actual structure.
Design Criteria
For columns subjected to bending under unfactored dead load, satisfy the minimum reinforcement requirements of Article 5.6.7, using half the exposure factor consistent with the site and other bridge elements.
Evaluate concrete tensile stress at Service I and Service IV for prestressed elements.
Detailing
Where lap splices are not possible see Chapter 5 - Other Designs, Section 6 – Non-Contact Lap Splices for reinforcing splice requirements.
Vehicular Collision
When the design choice is to redirect the collision load, follow the requirements given in Chapter 2 - Limit States and Loads. When the design choice is to provide structural resistance, follow the requirements in Chapter 4 - Substructure Design, Sections 7 - Columns for Multi-Column Bents.
No further analysis is required for columns with a gross cross-sectional area no less than 40 sq. ft., a minimum thickness of 5 ft. and column transverse reinforcement is composed of at least No. 4 ties at 12 in. maximum spacing or a No. 4 spiral at 9 in. maximum pitch.